INTRA-MOLECULAR EASILY POLARIZABLE HYDROGEN-BONDS IN DIAMIDES OF SUCCINIC AND ORTHO-PHTHALIC ACID

Succinic 1, o-phthalic 2 and oxalic 3 acid diamides (acetonitrile-d3 solutions) as well as their perchlorates were studied by proton magnetic resonance and infrared spectroscopy. With compounds 1 and 2 the protons are added to the N atoms but no intramolecular symmetrical N+H ... N ⇌ N ... H+N hydrogen bonds are formed. The NH+ groups build up intramolecular asymmetrical N+H ... OCN ⇌ N ... HOC+N hydrogen bonds. A double-minimum energy surface is present in these intramolecular bonds. They are easily polarizable. Hydrogen-bonded N+H groups are in equilibrium with non-hydrogen-bonded N+H groupgs. With the perchlorate of oxalic acid diamide 3, the protons are added to the O atoms of carbonyl groups. Most of the O+H groups formed interact only weakly with their environment. However, a few groups form intermolecular structurally symmetrical easily polarizable O+H ... O ⇌ O ... H+O hydrogen bonds. © 1979.